Mixed lineage leukemia (MLL) presents a heterogeneous group of acute myeloid leukemia and acute lymphoblastic leukemia bearing features of more than one hematopoietic cell lineage. MLL accounts for about 80% of infant acute leukemia cases (Tomizawa, D.; et. al. Leukemia, 2007, 21, 2258-63.) and 10% of all acute leukemia cases (Marschalek, R. Br. J. Haematol. 2011, 152, 141-54.). MLL leukemia patients have a poor prognosis with overall 5-year survival ratio around 35% (Dimartino, J. F.; Cleary, M. L., Br. J. Haematol. 1999, 106, 614-626; Pui, C., et al. Leukemia, 2003, 4, 700-706; Tomizawa, D.; et. al. Leukemia, 2007, 21, 2258-63.).
MLL is composed of heterogeneous cell lineages with different molecular biology, cell biology and immunology features. However, MLL does share a common feature, which involves the chromosomal rearrangement of Mixed Lineage Leukemia (MLL) gene. MLL gene locates on chromosome 11q23 and the encoded MLL protein is a homolog of Drosophila trithorax (Trx) (Thachuk, D. C.; et al. Cell, 1992, 71, 691-700.). Wild type MLL binds to regulatory regions of homeox (HOX) genes (Milne, T. A.; et al. Cancer Res., 2005, 65, 11367-74.) through the amino terminal fragment while the catalytic C-terminal domain catalyzes the Histone 3 lysine 4 (H3K4) methylation via interaction with WDR5 and up regulates target gene transcription (Nakamura, T.; et al. Mol. Cell, 2002, 10, 1119-28; Yokoyama, A. et al. Mol. Cell Biol., 2004, 24, 5639-49; Milne, T. A.; et al. Mol. Cell, 2002, 10, 1107-17). Wild type MLL in conjunction with WDR5 is required for maintenance HOX genes expression and is widely expressed not only during embryo development but also in adult tissues including myeloid and lymphoid cells (Yu, B. D.; et al. Proc. Natl. Acad. Sci., 1998, 95, 10632-10636.). Reciprocal translocations of MLL gene result in-frame fusion of the 5′-end MLL with the 3′-end of another partner gene. A common feature of MLL1 abnormality in leukemia is the preservation of one wild-type MLL1 allele. Currently, more than 80 partner genes have been identified, with MLL-AF4, MLL-AF9 and MLL-ENL being the three most frequently found fusion genes (Pui, C., et al. Leukemia, 2003, 4, 700-706; herein incorporated by reference in its entirety). Expression of MLL fusion proteins promotes over expression of target genes such as HOXA9 and MEIS1, which blocks differentiation, enhances blast expansion and ultimately leads to leukemic transformation (Caslini, C.; et al. Cancer Res., 2007, 67, 7275-83; Yokoyama, A.; et al. Cell, 2005, 123, 207-18.). The numerous chromosomal translocations of MLL gene and partner genes add to the complexity of MLL leukemia treatment. Although HOX9 and MEIS1 overexpression are commonly observed among MLL leukemia patients, each rearrangement leads to distinct dysregulated target gene expression patterns and downstream events (Slany, R. K., Haematologica, 2009, 94, 984-993). Clinical studies reveal that MLL of different chromosomal translocations are associated with different prognosis and are treated differently under current protocols (Tamai, H., et al. J. Clin. Exp. Hematop., 2010, 50, 91-98; Balgobind, B. V., et al. Leukemia, 2011, 8, 1239-1248; Pigazzi, M.; et al. Leukemia, 2011, 25, 560-563).
Intrinsic histone methyltransferase (HMT) activity of MLL1 is extremely low and requires a complex assembly of WDR5, RbBP5, ASH2L, and DPY30 protein partners for effective H3K4 trimethylation, the so-called WRAD complex (Patel, A.; et al. J. Biol. Chem., 2009, 284, 24242-56). The binding of MLL1 to WDR5 (WD40 repeat protein 5) is particularly critical for HMT activity and occurs through a conserved arginine containing motif on MLL1 called the “Win” or WDR5 interaction motif. Thus, targeting inhibitors of the MLL1-WDR5 interaction at the WIN site in order to block MLL1 methyltransferase activity could represent a promising therapeutic strategy for treating MLL leukemia patients. Peptidomimetics have been discovered that bind tightly to WDR5 at the MLL site, inhibit MLL1 methyltransferase activity, and block proliferation of MLL1 cells by inducing cell-cycle arrest, apoptosis, and myeloid differentiation (Cao, F.; et al. Molecular Cell, 2014, 53, 247-61., Karatas, H.; et al. J. Med. Chem., 2017, 60, 4818-4839.). In addition, altered gene expression patterns similar to MLL1 deletion are observed, supporting a role for MLL1 activity in regulating MLL1-dependent leukemia transcription. Thus, interruption of the WDR5-MLL1 interaction may be a useful strategy for treating patients with MLL leukemias. In addition to the highly characterized WDR5-MLL1 interaction, disruption of WDR5 with other recent transcription factors or displacement from chromatin itself could have a desirable benefit as a cancer treatment strategy. For example, WDR5 acts as a scaffold protein with the following chromatin complexes/structures, including histone H3 (via R2 residues, e.g. see Song, J.-J., et al. J. Biol. Chem. 2008, 283, 35258-64), NSL/MOF (Li, X., et al. Molecular and Cellular Biology, 2010, 30, 5335-47., Dias, J., et al. Genes & Development, 2014, 28, 929-942), C/EBPα p30 (Senisterra, G., et al. Biochem. J., 2013, 449, 151-159), c-MYC (Thomas, L. R.; et al. Molecular Cell, 2015, 58, 440-52., herein incorporated by reference in its entirety), and the NuRD complex (Ee, L.-S., et al. Stem Cell Reports, 2017, 8, 1488-96.). In addition, WDR5 expression levels have been reported to be correlative and connected to patient prognosis in several other cancer types, including neuroblastoma (Sun, Y. et al. Cancer Research, 2015, 75, 5143-54), breast cancer (Dai, X. et al. PLoSOne, 2015, 10, PMC4565643), bladder cancer (Chen, X. et al. Scientific Reports, 2015, 5, 8293), and colorectal cancer (Tan, X. et al. Cell Death & Disease, 2017, 8, PMC5386518). In addition, in an unbiased shRNA screen in human xenografts, WDR5 was identified as an important target in pancreatic cancer (Carugo, A. et al. Cell Reports, 2016, 16, 133-147.). Based on the growing number of complexes found which utilize WDR5 to maintain tumor fitness and growth, the emerging importance of WDR5 in several cancer types is not unexpected. In the case of the c-MYC-WDR5 interaction, the MYC oncoprotein utilizes a molecularly defined interaction with WDR5 to bind to its target genes on chromatin. MYC is overexpressed in a majority of malignancies and contributes to an estimated 70,000-100,000 cancer deaths per year in the United States. Thus, disruption of WDR5 from chromatin as a strategy to displace MYC from its target genes may provide a beneficial strategy to treat MYC-driven tumors.